The primary mission objective of the SLSTR instrument is to extend the long-term consistent set of global Sea Surface Temperature (SST) measurements.

SLSTR provides data continuity back to 1991 as its data permit the continuation of data-sets from previous instruments: ATSR on ERS-1, ATSR-2 on ERS-2 and AATSR on Envisat.

The SLSTR design incorporates the basic functionality of AATSR, with the addition of some new, more advanced, features. These include wider swath coverage which completely overlaps the OLCI swath, more spectral bands, and a spatial resolution of 0.5 km for visible and SWIR bands. Both the SLSTR and OLCI instruments require a clear view to the sun for calibration purposes and accommodating both on the same platform resulted in the SLSTR oblique view pointing backwards. This configuration is different to the ENVISAT AATSR configuration.

In addition, SLSTR using a suite of visible and infra-red radiance measurements provides land surface temperature, active fire monitoring, ice surface temperature, cloud, atmospheric aerosol, land surface, forestry and hydrology products in support of Copernicus services.

Following Envisat AATSR, the SLSTR instrument is a conical scanning imaging radiometer employing the along track scanning dual view technique to provide robust atmospheric correction over a dual-view swath. The instrument includes channels in the visible (VIS), thermal (TIR) and short wave (SWIR) infra-red spectrum.

A single SLSTR provides equivalent or better performance (see comparative table below) when compared to its predecessors in the following ways.

Increase of the dual view swath width from 500 to 740 km centred on the sub-satellite track gives a mean global coverage revisit time at the equator of 1.9 days (one spacecraft) or 0.9 days (two spacecraft).

Enlarged single view swath width of 1400 km provides a mean global coverage revisit time at the equator of 1 day (one spacecraft) or half a day (two spacecraft).

An on-ground resolution of 0.5 km at nadir (instead of 1 km) for all VIS and SWIR channels. Radiance measurements from these channels are used for both land and clouds daytime observations.

Two added channels (at wavelengths of 2.25 and 1.375 microns) in the SWIR band to allow improved cloud and aerosol detection to give more accurate SST/LST retrievals.

Two dedicated channels for fire and high temperature event monitoring at 1 km resolution (by extending the dynamic range of the 3.7 μm channel and including dedicated detectors at 10.8 μm that are capable of detecting fires at ~650 K without saturation).

A mission design lifetime of 7.5 years which is higher that of earlier instruments.

Performance

Parameters

SLSTR

AATSR & ATSR-1/2

Swaths

Nadir view

1 400 km

500 km

Dual view

740 km

500 km

Global coverage
revisit time

1 S/C (dual view)

1.9 days

7-14 days

0.9 days

-

1 day

7-14 days

0.5 days

-

SSI at SSP (km)

0.5 km VIS-SWIR
1 km IR-fire

1 km

Spectral channels
centre λ (µm)

VIS (not ATSR-1):
SWIR:
MWIR/TIR:
Fire-1/2:

0.555; 0.659; 0.865;
1.375; 1.610; 2.25;
3.74; 10.85; 12;
3.74; 10.85

0.555; 0.659; 0.865;
1.610;
3.74; 10.85; 12;
-

Radiometric
resolution

VIS (a=0.5%):
SWIR (a=0.5%):

SNR > 20
SNR > 20

SNR > 20
SNR > 20

MWIR (T=270K):
TIR (T=270K):
Fire-1 (<500 K):
Fire-2 (<400 K):

NeΔT < 80 mK
NeΔT < 50 mK
NeΔT < 1K
NeΔT < 0.5 K

NeΔT < 80 mK
NeΔT < 50 mK

Radiometric
accuracy

VIS-SWIR:
(a=2-100%)

< 2% (BOL)
< 5% (EOL)

< 5%

MWIR-TIR
(265-310K):
Fire (<500k):

< 0.1 k (goal)
< 3 K

< 0.1 K

Life time (in orbit)

7.5 years

AATSR: 5 year design,
operative since 2002;
ATSR-2: 3 year design,
operating from 1995 to 2008;
ATSR-1: 3 year design,
operating from 1991 to 2000

Table 1: Comparison of SLSTR specification with respect to previous AATSR and ATSR-1/2 instrument performance.
SSI is the spatial sampling interval at sub-satellite point (SSP), λ is central wavelength, a is top of atmosphere albedo, T is top of atmosphere brightness temperature, SNR is signal-to-noise ratio, and NEΔT is noise equivalent difference temperature.